1. Field of the Invention
The present invention relates to semiconductor device manufacturing technology. More specifically, the present invention relates to a method for preventing corrosion of a metal layer in a semiconductor device, thereby enabling improvement of the reliability and yield of a semiconductor device.
2. Description of the Related Art
Following the rapid progress of information and communication media such as a computer, the technology of manufacturing a semiconductor device has been rapidly developed. A semiconductor device has been developed toward higher integration, miniaturization, and higher operational speed.
Currently, aluminum or aluminum alloys are widely used as a wiring material for integrated circuits such as VLSI (Very Large-Scale Integration) devices, because of their superior electric conductivity and low prices. Processes of forming aluminum wiring generally comprise the steps of: forming an aluminum layer; coating and patterning a photoresist on the aluminum layer; etching an exposed portion of the aluminum layer (i.e., which is not covered with the photoresist) by means of plasma including chlorine; and removing the photoresist.
FIGS. 1a to 1c are cross-sectional views of a semiconductor device illustrating a conventional method for forming an aluminum wiring in the semiconductor device.
First, as shown in FIG. 1a, a photoresist is coated and patterned over a substrate 100 on which an oxide layer 102, barrier 104, aluminum layer 106 and antireflective coating 108 are formed in due order. Then, the antireflective coating 108, aluminum layer 106 and barrier 104 are dry-etched by means of Reactive Ion Etching (RIE) using a chlorine source gas such as Cl2, BCl3 and the like. Here, the patterned photoresist 110 is used as a mask for this etching process.
Next, as shown in FIG. 1b, the patterned photoresist 110 is removed by means of O2 plasma ashing process. At this time, corrosion defects 112 on a surface of aluminum layer 106 may result from circumstances such as fluorine, NH4OH, water, etc., working conditions of RIE, cleaning solutions used for removal of a photoresist, and especially chlorine residues occurring during the etch of aluminum layer 106. The corrosion defects 112 deteriorate the electrical performance of the semiconductor device or integrated circuit, or cause failures such as a short circuit thus decreasing the yield of manufacturing the semiconductor device.
In order to prevent such corrosion defects, the following methods are conventionally used. A first method involves cleaning the chlorine residues using deionized water, usually as a spray or in a bath. A second method involves evaporating the chlorine residues by heat treatment. A third method involves using a plasma containing fluorine.
However, the first method has little effect on removal of the chlorine residues, and generally does not prevent the corrosion of aluminum wirings in the long run. The second method may produce or result in problems such as hillock formation, segregation, or recrystallization, etc. when the temperature of the heat treatment is over 300° C., which are generally related to the low melting point of aluminum.
The third method has been disclosed in Japanese Patent Publication No. 83-12343 and Korean Patent Laid-Open Publication No. 2000-27241, which relates to a method for removing chlorine residues by means of an etching gas containing fluorine, and then removing a photoresist through an ashing process. However, this method may result in a problem where undercuts 114 on a titanium-containing layer (e.g., a TiN or TiW barrier) occur due to the fluorine-containing plasma, as shown in FIG. 1c. In addition, an underlying oxide layer may be damaged, and the aluminum may be changed to AlF3 (which can result in metal degradation). As a result, the reliability of semiconductor device may be conspicuously deteriorated.
In another method for manufacturing a semiconductor device, for the purpose of preventing reaction between chlorine residues and water when a substrate is exposed to air, an etching system is equipped with an ashing chamber so that a process of stripping a photoresist is performed in situ. Especially, before stripping a photoresist by means of plasma containing fluorine, chlorine residues are changed to hydrogen chloride (HCl) by means of H2O plasma, and then hydrogen chloride is exhausted by a pump, so that chlorine residues existing on surfaces of aluminum layer are generally removed. However, there are the same problems as the above-explained method has, which are caused by plasma containing fluorine.
To solve these problems, Korean Patent Publication No. 95-5351 discloses a method for preventing corrosion of a metal layer, comprising a plasma process using mixed gases of oxygen (O2) and ammonia (NH3). In addition, Korean Patent Laid Open Publication No. 2001-35852 discloses a method for preventing corrosion of a metal layer, comprising the step of exposing an object to plasma formed of mixed gases of H2N2 and oxygen. However, in case of using such mixed gases, a degree of preventing corrosion of a metal layer depends on a mixture ratio of gases. Moreover, these methods tend to have little effect on the prevention of corrosion.